Narcotics use has been identified as one of the major social problems of the twentieth century. Another significant social problem which has seen major growth during the last twenty five years is terrorism. Governments have sought to reduce acts of terrorism and the trafficking of narcotics by intensive searching of vessels, airplanes, and all forms of luggage and containers crossing national borders. Unfortunately, such search and seizure tactics have met with limited success.
The major impediment to search and seizure operations is the concealment of narcotics, explosives, and other forms of contraband within luggage, cargo, containers or even the structural elements of a transport vehicle. Often these containers or structural elements are made of metal or some other rigid material which, in order to be searched, must be damaged or destroyed.
Accordingly, there is a need for a non-destructive technique for the detection of narcotics, explosives, and other forms of contraband which may be concealed behind barriers or within a container.
Various techniques have been proposed to detect substances behind metal and other barriers. One such system is described in U.S. Pat. No. 4,864,142. That system utilizes the well-known phenomena of neutron resonance scattering, i.e., that a particular nuclei has large neutron cross sections for a neutron beam of a particular resonance energy characteristic of the particular nuclei. In that system, a tunable neutron source provides a beam of nuclei having the resonance energy of a nuclei desired to be detected. The source used is described in the patent at col. 10, lines 29-70, and utilizes a proton beam to generate neutrons. Since the protons are charged particles, their energy can be controlled by passing the beam through a controllable potential difference.
Other non-destructive search methods include the use of animals, sniffers, nuclear magnetic resonance, gamma ray scattering, and ultrasonics. Both animals and sniffers are unable to detect contraband in hermetically sealed containers. Gamma rays and NMR are not effective to penetrate metal barriers. Ultrasonics are useful for probing liquid containers but not very effective otherwise.
From the foregoing, it is apparent that a fast and reliable method of non-destructively searching within containers and through rigid barriers is desired.